Iron(II) and Ruthenium(II) Complexes Containing Bidentate, Tied-Back Diphosphonite Ligands. X-ray Structure of cis-FeMe 2 [(-OCH 2 CEt 2 CH 2 O-)PCH 2 CH 2 P(-OCH 2 CEt 2 CH 2 O-)] 2 Xinggao Fang, Brian L. Scott, John G. Watkin, and Gregory J. Kubas* Chemistry Division, MS J514, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Received December 1, 2000 Summary: trans-RuCl 2 (PP) 2 (2) and cis-FeCl 2 (PP) 2 (4) have been synthesized by the reaction of the diphospho- nite 1,2-bis((2,2-diethyl-1,3-propanedioxy)phosphino)- ethane (PP) with RuCl 2 (Ph 3 P) 3 and FeCl 2 , respectively. Complex 4 was converted to cis-FeMe 2 (PP) 2 (5), for which a molecular structure was obtained. Fe(II) and Ru(II) diphosphine complexes have been extensively studied for decades with various applica- tions, including small-molecule activation. 1 However, we have been surprised to find no literature report on analogous Fe(II) or Ru(II) complexes containing diphos- phonites. We have been interested in small-molecule activation on electrophilic transition-metal complexes with ligands that cannot offer intramolecular agostic C-H bond interaction. 2 Complexes of this nature can potentially coordinate extremely weak ligands such as alkanes, which otherwise cannot compete with entropi- cally favored agostic interactions. The new diphospho- nite 1,2-bis((2,2-diethyl-1,3-propanedioxy)phosphino)- ethane ligand (1; denoted as PP) appears to be a good ligand for such Fe(II) and Ru(II) complexes because of (1) its lack of internal agostic interaction capability and (2) weaker electron-donating ability compared to diphos- phine analogues. We report here on some Fe(II)/Ru(II) complexes containing ligand 1. As shown in Scheme 1, the ruthenium(II) dichloride 2 was synthesized by the reaction of RuCl 2 (Ph 3 P) 3 with 1, which was synthesized in high yield by the reaction of Cl 2 PCH 2 CH 2 PCl 2 with Et 2 C(CH 2 OH) 2 on the basis of the preparation of similar ligands. 3 The 31 P NMR chemical shifts of 1 and 2 are δ 174.0 and 203.8, respectively. Reaction of 2 with AgPF 6 in CH 2 Cl 2 apparently leads to removal of one chloride and formation of a white solid 3 that is not soluble in CH 2 Cl 2 but is slightly soluble in more coordinating acetone (Scheme 1). Complex 3 shows one 31 P NMR signal at δ 202.2 in acetone-d 6 , very close to the value of δ 203.8 for the neutral complex 2. The 1 H NMR shows two closely spaced triplets near δ 0.9 (methyl protons of two sets of inequivalent Et groups which are integrated as 24H total), and five other multiplet signals integrated as 8H each for the five inequivalent types of methylene protons (including those for the two inequivalent Et groups). This is similar to the pattern for 2, except the latter shows one signal (16H) at δ 4.03 instead of two for 3 at δ 3.99 and 4.27 (8H each). These signals apparently result from the methylene protons adjacent to oxygen on the diphos- phonite ligand, which presumably become inequivalent upon removal of a chloride to form 3. It is possible that the inequivalency results from one set of methylenes lying closer to the open coordination site than the other. Although the distances from the methylene C-H to the metal are much too long to be considered agostic, there may be a small perturbation leading to an NMR shift to lower field. Another possibility is that the “open” site may be weakly binding solvent or chloride from another molecule of 3, as will be discussed below. Solid 3, which did not react with the tied-back phosphite P(OCH 2 ) 3 CMe at room temperature, is likely to be a polymeric species bridged by chlorides to form chains, which may be at least partially broken on dissolving 3 in acetone. This is in contrast to analogous cationic diphosphine complexes such as [RuCl(dicyclo- hexylphosphinoethane) 2 ] + 4a and [RuCl(diphenylphos- phinoethane) 2 ] + , 4b which exist as discrete 16e five- coordinate molecules. The difference is possibly due to the fact that the Ru(II) cation in 3 is (1) more electro- philic (phosphonites are not as strongly donating as phosphines), (2) is less sterically crowded, and (3) has no internal agostic protection. All these factors encour- age coordination to Ru(II) from the chloride of another Ru(II) molecule, and for steric reasons (bulky diphos- phonites), the halide bridge may be linear, a rare but not unprecedented geometry. 5 Replacement of one or both chlorides in 2 with a group that does not contain lone pairs such as hydride or alkyl could lead to a 16e complex such as 3 that presumably would not oligomer- ize. However, reaction of the diphosphonite ligand 1 (1) For selected recent examples, see for Ru(II): (a) Schlaf, M.; Lough, A. J.; Morris, R. H. Organometallics 1997, 16, 1253. (b) Rocchini, E.; Mezzetti, A.; Ruegger, H.; Burckhardt, U.; Gramlich, V.; Del Zotto, A.; Martinuzzi, P. Rigo, P. Inorg. Chem. 1997, 36, 711. (c) Six, C.; Gabor, B.; Gorls, H.; Mynott, R.; Philipps, P.; Leitner, W. Organometallics 1999, 18, 3316. (d) Stoop, R. M.; Bauer, C.; Setz, P.; Worle, M.; Wong, T. Y. H.; Mezzetti, A.; Organometallics 1999, 18, 5691. (e) Martelletti, A.; Gramlich, V.; Zurcher, F.; Mezzetti, A. New J. Chem. 1999, 23, 199. For Fe(II): (f) Landau, S. E.; Morris, R. H.; Lough, A. J. Inorg. Chem. 1999, 38, 6060. (g) Bennett, M. A.; Ditzel, E. J.; Hunter, A. D.; Khan, K.; Kopp, M. R.; Neumann, H.; Robertson, G. B.; Zeh, H. J. Chem. Soc., Dalton Trans. 2000, 1733. (2) (a) Fang, X.-G.; Vincent, J. H.; Scott, B. L.; Kubas, G. J. J. Organomet. Chem. 2000, 609, 95. (b) Fang, X.-G.; Scott, B. L.; John, K. D.; Kubas, G. J. Organometallics 2000, 19, 4141. (3) Squires, M. E.; Sardellas, D. J.; Kool, L. B. Organometallics 1994, 13, 2970. (4) (a) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Pahor, N. B. J. Chem. Soc., Dalton Trans. 1989, 1045. (b) Chin, B.; Lough, A. J.; Morris, R. H.; Schweitzer, C. T.; D’Agostino, C. Inorg. Chem. 1994, 33, 6278. 2413 Organometallics 2001, 20, 2413-2416 10.1021/om001025+ CCC: $20.00 © 2001 American Chemical Society Publication on Web 05/01/2001